Proactive refresh of edge data word line for semi-circle drain side select gate

ABSTRACT

A memory apparatus and method of operation are provided. The apparatus includes memory cells connected to one of a plurality of word lines including at least one edge word line and a plurality of other data word lines. The memory cells are arranged in strings and configured to retain a threshold voltage corresponding to one of a plurality of data states. The memory apparatus also includes a control means coupled to the plurality of word lines and the strings. The control means is configured to identify the at least one edge word line. The control means is also configured to periodically apply a program voltage to the at least one edge word line to reprogram the memory cells associated with the at least one edge word line without erasing the memory cells associated with the at least one edge word line.

FIELD

This application relates to non-volatile memory apparatuses and theoperation of non-volatile memory apparatuses.

BACKGROUND

This section provides background information related to the technologyassociated with the present disclosure and, as such, is not necessarilyprior art.

Semi-circle drain side select gate (“SC-SGD”) memory technology offersseveral advantages, including reduced die size. In order to produceSC-SGD, etching technology is used to cut memory holes, thus giving themtheir semi-circular shape, and separating a block or row into severalstrings. Depending upon the process used to form the SC-SGD, certaininefficiencies can occur. For example, cutting a memory hole will removeat least some portions of the SC-SGD, such as the metal layer thatotherwise shields electrical fields from the channel and/or charge traplayer. Thus, the SC-SGD can be influenced by a “neighboring” electricfield, causing a parasitic transistor to leak along the SC-SGDtransistor. In some cases, this causes a sensing amplifier toincorrectly determine the SC-SGD is conducting, which can affect certainsensing operations. Also, due to etching variation, some dies may be cutdown to an SGD layer, while others may be cut down to layers formingdummy word lines. Consequently, data retention may be adversely affecteddue to charge loss in memory holes including the SC-SGD. Accordingly,there is a need for improved non-volatile memory apparatuses and methodsof operation.

SUMMARY

This section provides a general summary of the present disclosure and isnot a comprehensive disclosure of its full scope or all of its featuresand advantages.

An object of the present disclosure is to provide a memory apparatus anda method of operating the memory apparatus that address and overcome theabove-noted shortcomings.

Accordingly, it is an aspect of the present disclosure to provide anapparatus including memory cells connected to one of a plurality of wordlines including at least one edge word line and a plurality of otherdata word lines. The memory cells are arranged in strings and configuredto retain a threshold voltage corresponding to one of a plurality ofdata states. The memory apparatus also includes a control means coupledto the plurality of word lines and the strings. The control means isconfigured to identify the at least one edge word line. The controlmeans is also configured to periodically apply a program voltage to theat least one edge word line to reprogram the memory cells associatedwith the at least one edge word line without erasing the memory cellsassociated with the at least one edge word line.

According to another aspect of the disclosure, a controller incommunication with a memory apparatus including a memory apparatushaving memory cells connected to one of a plurality of word linesincluding at least one edge word line and a plurality of other data wordlines is also provided. The memory cells are arranged in strings and areconfigured to retain a threshold voltage corresponding to one of aplurality of data states. The controller is configured to identify theat least one edge word line. The controller is also configured toinstruct the memory apparatus to periodically apply a program voltage tothe at least one edge word line to reprogram the memory cells associatedwith the at least one edge word line without erasing the memory cellsassociated with the at least one edge word line.

According to an additional aspect of the disclosure a method ofoperating a memory apparatus is provided. The memory apparatus includesmemory cells connected to one of a plurality of word lines including atleast one edge word line and a plurality of other data word lines. Thememory cells are arranged in strings and are configured to retain athreshold voltage corresponding to one of a plurality of data states.The method includes the step of identifying the at least one edge wordline. The method also includes the step of periodically applying aprogram voltage to the at least one edge word line to reprogram thememory cells associated with the at least one edge word line withouterasing the memory cells associated with the at least one edge wordline.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1A is a block diagram of an example memory device according toaspects of the disclosure;

FIG. 1B is a block diagram of an example control circuit that includes aprogramming circuit, a counting circuit, and a determination circuitaccording to aspects of the disclosure;

FIG. 2 illustrates schematic views of three types of memoryarchitectures utilizing staggered memory strings according to aspects ofthe disclosure;

FIG. 3A illustrates a cross-sectional view of example floating gatememory cells in NAND strings according to aspects of the disclosure;

FIG. 3B illustrates a cross-sectional view along a contact line shown inFIG. 3A according to aspects of the disclosure;

FIGS. 4A and 4B illustrate non-volatile memory in which acharge-trapping memory cell uses a non-conductive dielectric material inplace of a conductive floating gate to store charge in a non-volatilemanner according to aspects of the disclosure;

FIG. 5 illustrates an example block diagram of the sense block of FIG. 1according to aspects of the disclosure;

FIG. 6A is a perspective view of a set of blocks in an examplethree-dimensional configuration of the memory array of FIG. 1 accordingto aspects of the disclosure;

FIG. 6B illustrates an example cross-sectional view of a portion of oneof the blocks of FIG. 6A according to aspects of the disclosure;

FIG. 6C illustrates a plot of memory hole diameter in the stack of FIG.6B according to aspects of the disclosure;

FIG. 6D illustrates a close-up view of the region of the stack of FIG.6B according to aspects of the disclosure;

FIG. 7A illustrates a schematic plan view of a memory array with aplurality of memory holes according to aspects of the disclosure;

FIG. 7B illustrates a cross-sectional view of the memory array accordingto aspects of the disclosure;

FIGS. 8A and 8B illustrate an alternate memory structure with no dummyholes according to aspects of the disclosure;

FIG. 9 depicts an example set of threshold voltage distributionsaccording to aspects of the disclosure;

FIG. 10 shows a cross-sectional top view of memory holes taken at adrain-side select gate layer and an edge word line layer according toaspects of the disclosure;

FIG. 11 shows threshold voltage distributions and corresponding data ormemory states before and after high temperature data retention testingfor an example memory apparatus according to aspects of the disclosure;

FIG. 12 shows another cross-sectional top view of memory holes taken atthe drain-side select gate layer, a layer corresponding to one of theplurality of other data word lines, and the edge word line layeraccording to aspects of the disclosure;

FIG. 13 shows the plurality of bit lines connecting to memory holes orstrings having full-circle and semi-circle drain-side select gates andthreshold voltage distributions for memory cells in the strings ormemory holes associated with the semi-circle rows and full-circle rowsafter programming, after high temperature data retention testing,determining the edge higher data state quantity greater less than anedge highest data state threshold, and after reprogramming the memorycells associated with the at least one edge word line without erasingthe memory cells associated with the at least one edge word lineaccording to aspects of the disclosure; and

FIG. 14 illustrates steps of a method of operating a memory apparatusaccording to aspects of the disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DETAILED DESCRIPTION

In the following description, details are set forth to provide anunderstanding of the present disclosure. In some instances, certaincircuits, structures and techniques have not been described or shown indetail in order not to obscure the disclosure.

In general, the present disclosure relates to non-volatile memoryapparatuses of the type well-suited for use in many applications. Thenon-volatile memory apparatus and associated methods of operation ofthis disclosure will be described in conjunction with one or moreexample embodiments. However, the specific example embodiments disclosedare merely provided to describe the inventive concepts, features,advantages and objectives with sufficient clarity to permit thoseskilled in this art to understand and practice the disclosure.Specifically, the example embodiments are provided so that thisdisclosure will be thorough, and will fully convey the scope to thosewho are skilled in the art. Numerous specific details are set forth suchas examples of specific components, devices, and methods, to provide athorough understanding of embodiments of the present disclosure. It willbe apparent to those skilled in the art that specific details need notbe employed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

In some memory devices or apparatuses, memory cells are joined to oneanother such as in NAND strings in a block or sub-block. Each NANDstring comprises a number of memory cells connected in series betweenone or more drain-side SG transistors (SGD transistors), on a drain-sideof the NAND string which is connected to a bit line, and one or moresource-side SG transistors (SGS transistors), on a source-side of theNAND string which is connected to a source line. Further, the memorycells can be arranged with a common control gate line (e.g., word line)which acts a control gate. A set of word lines extends from the sourceside of a block to the drain side of a block. Memory cells can beconnected in other types of strings and in other ways as well.

In a 3D memory structure, the memory cells may be arranged in verticalstrings in a stack, where the stack comprises alternating conductive anddielectric layers. The conductive layers act as word lines which areconnected to the memory cells. The memory cells can include data memorycells, which are eligible to store user data, and dummy or non-datamemory cells which are ineligible to store user data.

Before programming certain non-volatile memory devices, the memory cellsare typically erased. For some devices, the erase operation removeselectrons from the floating gate of the memory cell being erased.Alternatively, the erase operation removes electrons from thecharge-trapping layer.

Each memory cell may be associated with a data state according to writedata in a program command. Based on its data state, a memory cell willeither remain in the erased state or be programmed to a programmed datastate. For example, in a three bit per cell memory device, there areeight data states including the erased state and the programmed state(see e.g., FIG. 9 ).

During a program operation, the memory cells are programmed according toa word line programming order. For example, the programming may start atthe word line at the source side of the block and proceed to the wordline at the drain side of the block. In one approach, each word line iscompletely programmed before programming a next word line. For example,a first word line, WL0, is programmed using one or more programmingpulses until the programming is completed. Next, a second word line,WL1, is programmed using one or more programming pulses until theprogramming is completed, and so forth. A programming pulse may includea set of increasing program voltages which are applied to the word linein respective program loops or program-verify iterations. Verifyoperations or stages may be performed after each program voltage todetermine whether the memory cells have completed programming. Whenprogramming is completed for a memory cell, it can be inhibited fromfurther programming while programming continues for other memory cellsin subsequent program loops.

When creating various rows and strings for a memory structure, a cuttingoperation (e.g., shallow hole etch, or SHE) can be used. The SHE cut candivide a block (in memory) into multiple strings within the block. Whilethe SHE can form/define the strings, the SHE cut can further separate astring, i.e., cut the edge memory holes in a string into half (orapproximately two equal halves). In this regard, both the SGD and thechannel are split. However, this operation will cut away parts of somerows of memory holes, resulting in semi-circle drain side select gate(“SC-SGD”). Using SHE cutting operation, the degree/amount/percentage ofcutting can vary. As a result, some top layer SGD (“SGDT”) on SC-SGD arecut to a greater degree than others. In other words, the amount ofmaterial removed from some SC-SGD memory holes can be greater than theamount removed from others and may cause the SHE cut to extend down toone or more dummy word line layers. When the SHE cut is closer to thedata word lines (i.e., deeper), data retention issues can arise. Thus,described herein are memory systems or apparatuses and correspondingmethods of operation directed to refresh data associated with one ormore word lines to improve data retention.

The several aspects of the present disclosure may be embodied in theform of an apparatus, system, method, or computer program process.Therefore, aspects of the present disclosure may be entirely in the formof a hardware embodiment or a software embodiment (including but notlimited to firmware, resident software, micro-code, or the like), or maybe a combination of both hardware and software components that maygenerally be referred to collectively as a “circuit,” “module,”“apparatus,” or “system.” Further, various aspects of the presentdisclosure may be in the form of a computer program process that isembodied, for example, in one or more non-transitory computer-readablestorage media storing computer-readable and/or executable program code.

Additionally, various terms are used herein to refer to particularsystem components. Different companies may refer to a same or similarcomponent by different names and this description does not intend todistinguish between components that differ in name but not in function.To the extent that various functional units described in the followingdisclosure are referred to as “modules,” such a characterization isintended to not unduly restrict the range of potential implementationmechanisms. For example, a “module” could be implemented as a hardwarecircuit that includes customized very-large-scale integration (VLSI)circuits or gate arrays, or off-the-shelf semiconductors that includelogic chips, transistors, or other discrete components. In a furtherexample, a module may also be implemented in a programmable hardwaredevice such as a field programmable gate array (FPGA), programmablearray logic, a programmable logic device, or the like. Furthermore, amodule may also, at least in part, be implemented by software executedby various types of processors. For example, a module may comprise asegment of executable code constituting one or more physical or logicalblocks of computer instructions that translate into an object, process,or function. Also, it is not required that the executable portions ofsuch a module be physically located together, but rather, may comprisedisparate instructions that are stored in different locations and which,when executed together, comprise the identified module and achieve thestated purpose of that module. The executable code may comprise just asingle instruction or a set of multiple instructions, as well as bedistributed over different code segments, or among different programs,or across several memory devices, etc. In a software, or partialsoftware, module implementation, the software portions may be stored onone or more computer-readable and/or executable storage media thatinclude, but are not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor-based system, apparatus, ordevice, or any suitable combination thereof. In general, for purposes ofthe present disclosure, a computer-readable and/or executable storagemedium may be comprised of any tangible and/or non-transitory mediumthat is capable of containing and/or storing a program for use by or inconnection with an instruction execution system, apparatus, processor,or device.

Similarly, for the purposes of the present disclosure, the term“component” may be comprised of any tangible, physical, andnon-transitory device. For example, a component may be in the form of ahardware logic circuit that is comprised of customized VLSI circuits,gate arrays, or other integrated circuits, or is comprised ofoff-the-shelf semiconductors that include logic chips, transistors, orother discrete components, or any other suitable mechanical and/orelectronic devices. In addition, a component could also be implementedin programmable hardware devices such as field programmable gate arrays(FPGA), programmable array logic, programmable logic devices, etc.Furthermore, a component may be comprised of one or more silicon-basedintegrated circuit devices, such as chips, die, die planes, andpackages, or other discrete electrical devices, in an electricalcommunication configuration with one or more other components viaelectrical conductors of, for example, a printed circuit board (PCB) orthe like. Accordingly, a module, as defined above, may in certainembodiments, be embodied by or implemented as a component and, in someinstances, the terms module and component may be used interchangeably.

Where the term “circuit” is used herein, it includes one or moreelectrical and/or electronic components that constitute one or moreconductive pathways that allow for electrical current to flow. A circuitmay be in the form of a closed-loop configuration or an open-loopconfiguration. In a closed-loop configuration, the circuit componentsmay provide a return pathway for the electrical current. By contrast, inan open-looped configuration, the circuit components therein may stillbe regarded as forming a circuit despite not including a return pathwayfor the electrical current. For example, an integrated circuit isreferred to as a circuit irrespective of whether the integrated circuitis coupled to ground (as a return pathway for the electrical current) ornot. In certain exemplary embodiments, a circuit may comprise a set ofintegrated circuits, a sole integrated circuit, or a portion of anintegrated circuit. For example, a circuit may include customized VLSIcircuits, gate arrays, logic circuits, and/or other forms of integratedcircuits, as well as may include off-the-shelf semiconductors such aslogic chips, transistors, or other discrete devices. In a furtherexample, a circuit may comprise one or more silicon-based integratedcircuit devices, such as chips, die, die planes, and packages, or otherdiscrete electrical devices, in an electrical communicationconfiguration with one or more other components via electricalconductors of, for example, a printed circuit board (PCB). A circuitcould also be implemented as a synthesized circuit with respect to aprogrammable hardware device such as a field programmable gate array(FPGA), programmable array logic, and/or programmable logic devices,etc. In other exemplary embodiments, a circuit may comprise a network ofnon-integrated electrical and/or electronic components (with or withoutintegrated circuit devices). Accordingly, a module, as defined above,may in certain embodiments, be embodied by or implemented as a circuit.

It will be appreciated that example embodiments that are disclosedherein may be comprised of one or more microprocessors and particularstored computer program instructions that control the one or moremicroprocessors to implement, in conjunction with certain non-processorcircuits and other elements, some, most, or all of the functionsdisclosed herein. Alternatively, some or all functions could beimplemented by a state machine that has no stored program instructions,or in one or more application-specific integrated circuits (ASICs) orfield-programmable gate arrays (FPGAs), in which each function or somecombinations of certain of the functions are implemented as customlogic. A combination of these approaches may also be used. Further,references below to a “controller” shall be defined as comprisingindividual circuit components, an application-specific integratedcircuit (ASIC), a microcontroller with controlling software, a digitalsignal processor (DSP), a field programmable gate array (FPGA), and/or aprocessor with controlling software, or combinations thereof.

Further, the terms “program,” “software,” “software application,” andthe like as may be used herein, refer to a sequence of instructions thatis designed for execution on a computer-implemented system. Accordingly,a “program,” “software,” “application,” “computer program,” or “softwareapplication” may include a subroutine, a function, a procedure, anobject method, an object implementation, an executable application, anapplet, a servlet, a source code, an object code, a sharedlibrary/dynamic load library and/or other sequence of specificinstructions that is designed for execution on a computer system.

Additionally, the terms “couple,” “coupled,” or “couples,” where may beused herein, are intended to mean either a direct or an indirectconnection. Thus, if a first device couples, or is coupled to, a seconddevice, that connection may be by way of a direct connection or throughan indirect connection via other devices (or components) andconnections.

Regarding, the use herein of terms such as “an embodiment,” “oneembodiment,” an “exemplary embodiment,” a “particular embodiment,” orother similar terminology, these terms are intended to indicate that aspecific feature, structure, function, operation, or characteristicdescribed in connection with the embodiment is found in at least oneembodiment of the present disclosure. Therefore, the appearances ofphrases such as “in one embodiment,” “in an embodiment,” “in anexemplary embodiment,” etc., may, but do not necessarily, all refer tothe same embodiment, but rather, mean “one or more but not allembodiments” unless expressly specified otherwise. Further, the terms“comprising,” “having,” “including,” and variations thereof, are used inan open-ended manner and, therefore, should be interpreted to mean“including, but not limited to . . . ” unless expressly specifiedotherwise. Also, an element that is preceded by “comprises . . . a” doesnot, without more constraints, preclude the existence of additionalidentical elements in the subject process, method, system, article, orapparatus that includes the element.

The terms “a,” “an,” and “the” also refer to “one or more” unlessexpressly specified otherwise. In addition, the phrase “at least one ofA and B” as may be used herein and/or in the following claims, whereby Aand B are variables indicating a particular object or attribute,indicates a choice of A or B, or both A and B, similar to the phrase“and/or.” Where more than two variables are present in such a phrase,this phrase is hereby defined as including only one of the variables,any one of the variables, any combination (or sub-combination) of any ofthe variables, and all of the variables.

Further, where used herein, the term “about” or “approximately” appliesto all numeric values, whether or not explicitly indicated. These termsgenerally refer to a range of numeric values that one of skill in theart would consider equivalent to the recited values (e.g., having thesame function or result). In certain instances, these terms may includenumeric values that are rounded to the nearest significant figure.

In addition, any enumerated listing of items that is set forth hereindoes not imply that any or all of the items listed are mutuallyexclusive and/or mutually inclusive of one another, unless expresslyspecified otherwise. Further, the term “set,” as used herein, shall beinterpreted to mean “one or more,” and in the case of “sets,” shall beinterpreted to mean multiples of (or a plurality of) “one or more,”“ones or more,” and/or “ones or mores” according to set theory, unlessexpressly specified otherwise.

In the detailed description that follows, reference is made to theappended drawings, which form a part thereof. It is recognized that theforegoing summary is illustrative only and is not intended to belimiting in any manner. In addition to the illustrative aspects, exampleembodiments, and features described above, additional aspects, exemplaryembodiments, and features will become apparent by reference to thedrawings and the detailed description below. The description of elementsin each figure may refer to elements of preceding and/or followingfigures. Like reference numerals may refer to like elements in thefigures, including alternate exemplary embodiments of like elements.

FIG. 1A is a block diagram of an example memory device. The memorydevice 100 may include one or more memory die 108. The memory die 108includes a memory structure 126 of memory cells, such as an array ofmemory cells, control circuitry 110, and read/write circuits 128. Thememory structure 126 is addressable by word lines via a row decoder 124and by bit lines via a column decoder 132. The read/write circuits 128include multiple sense blocks SB1, SB2, . . . SBp (sensing circuitry)and allow a page of memory cells to be read or programmed in parallel.Typically, a controller 122 is included in the same memory device 100(e.g., a removable storage card) as the one or more memory die 108.Commands and data are transferred between the host 140 and controller122 via a data bus 120, and between the controller and the one or morememory die 108 via lines 118.

The memory structure 126 can be two-dimensional or three-dimensional.The memory structure 126 may comprise one or more array of memory cellsincluding a three-dimensional array. The memory structure 126 maycomprise a monolithic three-dimensional memory structure in whichmultiple memory levels are formed above (and not in) a single substrate,such as a wafer, with no intervening substrates. The memory structure126 may comprise any type of non-volatile memory that is monolithicallyformed in one or more physical levels of arrays of memory cells havingan active area disposed above a silicon substrate. The memory structure126 may be in a non-volatile memory device having circuitry associatedwith the operation of the memory cells, whether the associated circuitryis above or within the substrate.

The control circuitry 110 cooperates with the read/write circuits 128 toperform memory operations on the memory structure 126, and includes astate machine 112, an on-chip address decoder 114, and a power controlmodule 116. The state machine 112 provides chip-level control of memoryoperations.

A storage region 113 may, for example, be provided for programmingparameters. The programming parameters may include a program voltage, aprogram voltage bias, position parameters indicating positions of memorycells, contact line connector thickness parameters, a verify voltage,and/or the like. The position parameters may indicate a position of amemory cell within the entire array of NAND strings, a position of amemory cell as being within a particular NAND string group, a positionof a memory cell on a particular plane, and/or the like. The contactline connector thickness parameters may indicate a thickness of acontact line connector, a substrate or material that the contact lineconnector is comprised of, and/or the like.

The on-chip address decoder 114 provides an address interface betweenthat used by the host or a memory controller to the hardware addressused by the decoders 124 and 132. The power control module 116 controlsthe power and voltages supplied to the word lines and bit lines duringmemory operations. It can include drivers for word lines, SGS and SGDtransistors, and source lines. The sense blocks can include bit linedrivers, in one approach. An SGS transistor is a select gate transistorat a source end of a NAND string, and an SGD transistor is a select gatetransistor at a drain end of a NAND string.

In some embodiments, some of the components can be combined. In variousdesigns, one or more of the components (alone or in combination), otherthan memory structure 126, can be thought of as at least one controlcircuit which is configured to perform the actions described herein. Forexample, a control circuit may include any one of, or a combination of,control circuitry 110, state machine 112, decoders 114/132, powercontrol module 116, sense blocks SBb, SB2, . . . , SBp, read/writecircuits 128, controller 122, and so forth.

The control circuits can include a programming circuit configured toperform a program and verify operation for one set of memory cells,wherein the one set of memory cells comprises memory cells assigned torepresent one data state among a plurality of data states and memorycells assigned to represent another data state among the plurality ofdata states; the program and verify operation comprising a plurality ofprogram and verify iterations; and in each program and verify iteration,the programming circuit performs programming for the one word line afterwhich the programming circuit applies a verification signal to the oneword line. The control circuits can also include a counting circuitconfigured to obtain a count of memory cells which pass a verify testfor the one data state. The control circuits can also include adetermination circuit configured to determine, based on an amount bywhich the count exceeds a threshold, a particular program and verifyiteration among the plurality of program and verify iterations in whichto perform a verify test for another data state for the memory cellsassigned to represent another data state.

For example, FIG. 1B is a block diagram of an example control circuit150 which comprises a programming circuit 151, a counting circuit 152,and a determination circuit 153.

The off-chip controller 122 may comprise a processor 122 c, storagedevices (memory) such as ROM 122 a and RAM 122 b and an error-correctioncode (ECC) engine 245. The ECC engine can correct a number of readerrors which are caused when the upper tail of a Vth distributionbecomes too high. However, uncorrectable errors may exist in some cases.The techniques provided herein reduce the likelihood of uncorrectableerrors.

The storage device(s) 122 a, 122 b comprise, code such as a set ofinstructions, and the processor 122 c is operable to execute the set ofinstructions to provide the functionality described herein. Alternatelyor additionally, the processor 122 c can access code from a storagedevice 126 a of the memory structure 126, such as a reserved area ofmemory cells in one or more word lines. For example, code can be used bythe controller 122 to access the memory structure 126 such as forprogramming, read and erase operations. The code can include boot codeand control code (e.g., set of instructions). The boot code is softwarethat initializes the controller 122 during a booting or startup processand enables the controller 122 to access the memory structure 126. Thecode can be used by the controller 122 to control one or more memorystructures 126. Upon being powered up, the processor 122 c fetches theboot code from the ROM 122 a or storage device 126 a for execution, andthe boot code initializes the system components and loads the controlcode into the RAM 122 b. Once the control code is loaded into the RAM122 b, it is executed by the processor 122 c. The control code includesdrivers to perform basic tasks such as controlling and allocatingmemory, prioritizing the processing of instructions, and controllinginput and output ports.

Generally, the control code can include instructions to perform thefunctions described herein including the steps of the flowchartsdiscussed further below and provide the voltage waveforms includingthose discussed further below.

In one embodiment, the host is a computing device (e.g., laptop,desktop, smartphone, tablet, digital camera) that includes one or moreprocessors, one or more processor readable storage devices (RAM, ROM,flash memory, hard disk drive, solid state memory) that store processorreadable code (e.g., software) for programming the one or moreprocessors to perform the methods described herein. The host may alsoinclude additional system memory, one or more input/output interfacesand/or one or more input/output devices in communication with the one ormore processors.

Other types of non-volatile memory in addition to NAND flash memory canalso be used.

Semiconductor memory devices include volatile memory devices, such asdynamic random access memory (“DRAM”) or static random access memory(“SRAM”) devices, non-volatile memory devices, such as resistive randomaccess memory (“ReRAM”), electrically erasable programmable read onlymemory (“EEPROM”), flash memory (which can also be considered a subsetof EEPROM), ferroelectric random access memory (“FRAM”), andmagnetoresistive random access memory (“MRAM”), and other semiconductorelements capable of storing information. Each type of memory device mayhave different configurations. For example, flash memory devices may beconfigured in a NAND or a NOR configuration.

The memory devices can be formed from passive and/or active elements, inany combinations. By way of non-limiting example, passive semiconductormemory elements include ReRAM device elements, which in some embodimentsinclude a resistivity switching storage element, such as an anti-fuse orphase change material, and optionally a steering element, such as adiode or transistor. Further by way of non-limiting example, activesemiconductor memory elements include EEPROM and flash memory deviceelements, which in some embodiments include elements containing a chargestorage region, such as a floating gate, conductive nanoparticles, or acharge storage dielectric material.

Multiple memory elements may be configured so that they are connected inseries or so that each element is individually accessible. By way ofnon-limiting example, flash memory devices in a NAND configuration (NANDmemory) typically contain memory elements connected in series. A NANDstring is an example of a set of series-connected transistors comprisingmemory cells and SG transistors.

A NAND memory array may be configured so that the array is composed ofmultiple memory strings in which a string is composed of multiple memoryelements sharing a single bit line and accessed as a group.Alternatively, memory elements may be configured so that each element isindividually accessible, e.g., a NOR memory array. NAND and NOR memoryconfigurations are examples, and memory elements may be otherwiseconfigured. The semiconductor memory elements located within and/or overa substrate may be arranged in two or three dimensions, such as atwo-dimensional memory structure or a three-dimensional memorystructure.

In a two-dimensional memory structure, the semiconductor memory elementsare arranged in a single plane or a single memory device level.Typically, in a two-dimensional memory structure, memory elements arearranged in a plane (e.g., in an x-y direction plane) which extendssubstantially parallel to a major surface of a substrate that supportsthe memory elements. The substrate may be a wafer over or in which thelayer of the memory elements is formed or it may be a carrier substratewhich is attached to the memory elements after they are formed. As anon-limiting example, the substrate may include a semiconductor such assilicon.

The memory elements may be arranged in the single memory device level inan ordered array, such as in a plurality of rows and/or columns.However, the memory elements may be arrayed in non-regular ornon-orthogonal configurations. The memory elements may each have two ormore electrodes or contact lines, such as bit lines and word lines.

A three-dimensional memory array is arranged so that memory elementsoccupy multiple planes or multiple memory device levels, thereby forminga structure in three dimensions (i.e., in the x, y and z directions,where the z-direction is substantially perpendicular and the x- andy-directions are substantially parallel to the major surface of thesubstrate).

As a non-limiting example, a three-dimensional memory structure may bevertically arranged as a stack of multiple two-dimensional memory devicelevels. As another non-limiting example, a three-dimensional memoryarray may be arranged as multiple vertical columns (e.g., columnsextending substantially perpendicular to the major surface of thesubstrate, i.e., in the y direction) with each column having multiplememory elements. The columns may be arranged in a two-dimensionalconfiguration, e.g., in an x-y plane, resulting in a three-dimensionalarrangement of memory elements with elements on multiple verticallystacked memory planes. Other configurations of memory elements in threedimensions can also constitute a three-dimensional memory array.

By way of non-limiting example, in a three-dimensional array of NANDstrings, the memory elements may be coupled together to form a NANDstring within a single horizontal (e.g., x-y) memory device level.Alternatively, the memory elements may be coupled together to form avertical NAND string that traverses across multiple horizontal memorydevice levels. Other three-dimensional configurations can be envisionedwherein some NAND strings contain memory elements in a single memorylevel while other strings contain memory elements which span throughmultiple memory levels. Three-dimensional memory arrays may also bedesigned in a NOR configuration and in a ReRAM configuration.

Typically, in a monolithic three-dimensional memory array, one or morememory device levels are formed above a single substrate. Optionally,the monolithic three-dimensional memory array may also have one or morememory layers at least partially within the single substrate. As anon-limiting example, the substrate may include a semiconductor such assilicon. In a monolithic three-dimensional array, the layersconstituting each memory device level of the array are typically formedon the layers of the underlying memory device levels of the array.However, layers of adjacent memory device levels of a monolithicthree-dimensional memory array may be shared or have intervening layersbetween memory device levels.

Then again, two-dimensional arrays may be formed separately and thenpackaged together to form a non-monolithic memory device having multiplelayers of memory. For example, non-monolithic stacked memories can beconstructed by forming memory levels on separate substrates and thenstacking the memory levels atop each other. The substrates may bethinned or removed from the memory device levels before stacking, but asthe memory device levels are initially formed over separate substrates,the resulting memory arrays are not monolithic three-dimensional memoryarrays. Further, multiple two-dimensional memory arrays orthree-dimensional memory arrays (monolithic or non-monolithic) may beformed on separate chips and then packaged together to form astacked-chip memory device.

FIG. 2 illustrates schematic views of three types of memoryarchitectures utilizing staggered memory strings. For example, referencenumber 201 shows a schematic view of a first example memoryarchitecture, reference number 203 shows a schematic view of a secondexample memory architecture, and reference number 205 shows a schematicview of a third example memory architecture. In some embodiments, asshown, the memory architecture may include an array of staggered NANDstrings.

FIG. 2 illustrates blocks 200, 210 of memory cells in an exampletwo-dimensional configuration of the memory array 126 of FIG. 1 . Thememory array 126 can include many such blocks 200, 210. Each exampleblock 200, 210 includes a number of NAND strings and respective bitlines, e.g., BL0, BL1, . . . which are shared among the blocks. EachNAND string is connected at one end to a drain-side select gate (SGD),and the control gates of the drain select gates are connected via acommon SGD line. The NAND strings are connected at their other end to asource-side select gate (SGS) which, in turn, is connected to a commonsource line 220. Sixteen word lines, for example, WL0-WL15, extendbetween the SGSs and the SGDs. In some cases, dummy word lines, whichcontain no user data, can also be used in the memory array adjacent tothe select gate transistors. Such dummy word lines can shield the edgedata word line from certain edge effects.

One type of non-volatile memory which may be provided in the memoryarray is a floating gate memory, such as of the type shown in FIGS. 3Aand 3B. However, other types of non-volatile memory can also be used. Asdiscussed in further detail below, in another example shown in FIGS. 4Aand 4B, a charge-trapping memory cell uses a non-conductive dielectricmaterial in place of a conductive floating gate to store charge in anon-volatile manner. A triple layer dielectric formed of silicon oxide,silicon nitride and silicon oxide (“ONO”) is sandwiched between aconductive control gate and a surface of a semi-conductive substrateabove the memory cell channel. The cell is programmed by injectingelectrons from the cell channel into the nitride, where they are trappedand stored in a limited region. This stored charge then changes thethreshold voltage of a portion of the channel of the cell in a mannerthat is detectable. The cell is erased by injecting hot holes into thenitride. A similar cell can be provided in a split-gate configurationwhere a doped polysilicon gate extends over a portion of the memory cellchannel to form a separate select transistor.

In another approach, NROM cells are used. Two bits, for example, arestored in each NROM cell, where an ONO dielectric layer extends acrossthe channel between source and drain diffusions. The charge for one databit is localized in the dielectric layer adjacent to the drain, and thecharge for the other data bit localized in the dielectric layer adjacentto the source. Multi-state data storage is obtained by separatelyreading binary states of the spatially separated charge storage regionswithin the dielectric. Other types of non-volatile memory are alsoknown.

FIG. 3A illustrates a cross-sectional view of example floating gatememory cells 300, 310, 320 in NAND strings. In this Figure, a bit lineor NAND string direction goes into the page, and a word line directiongoes from left to right. As an example, word line 324 extends acrossNAND strings which include respective channel regions 306, 316 and 326.The memory cell 300 includes a control gate 302, a floating gate 304, atunnel oxide layer 305 and the channel region 306. The memory cell 310includes a control gate 312, a floating gate 314, a tunnel oxide layer315 and the channel region 316. The memory cell 320 includes a controlgate 322, a floating gate 321, a tunnel oxide layer 325 and the channelregion 326. Each memory cell 300, 310, 320 is in a different respectiveNAND string. An inter-poly dielectric (IPD) layer 328 is alsoillustrated. The control gates 302, 312, 322 are portions of the wordline. A cross-sectional view along contact line connector 329 isprovided in FIG. 3B.

The control gate 302, 312, 322 wraps around the floating gate 304, 314,321, increasing the surface contact area between the control gate 302,312, 322 and floating gate 304, 314, 321. This results in higher IPDcapacitance, leading to a higher coupling ratio which makes programmingand erase easier. However, as NAND memory devices are scaled down, thespacing between neighboring cells 300, 310, 320 becomes smaller so thereis almost no space for the control gate 302, 312, 322 and the IPD layer328 between two adjacent floating gates 302, 312, 322.

As an alternative, as shown in FIGS. 4A and 4B, the flat or planarmemory cell 400, 410, 420 has been developed in which the control gate402, 412, 422 is flat or planar; that is, it does not wrap around thefloating gate and its only contact with the charge storage layer 428 isfrom above it. In this case, there is no advantage in having a tallfloating gate. Instead, the floating gate is made much thinner. Further,the floating gate can be used to store charge, or a thin charge traplayer can be used to trap charge. This approach can avoid the issue ofballistic electron transport, where an electron can travel through thefloating gate after tunneling through the tunnel oxide duringprogramming.

FIG. 4A depicts a cross-sectional view of example charge-trapping memorycells 400, 410, 420 in NAND strings. The view is in a word linedirection of memory cells 400, 410, 420 comprising a flat control gateand charge-trapping regions as a two-dimensional example of memory cells400, 410, 420 in the memory cell array 126 of FIG. 1 . Charge-trappingmemory can be used in NOR and NAND flash memory device. This technologyuses an insulator such as an SiN film to store electrons, in contrast toa floating-gate MOSFET technology which uses a conductor such as dopedpolycrystalline silicon to store electrons. As an example, a word line424 extends across NAND strings which include respective channel regions406, 416, 426. Portions of the word line provide control gates 402, 412,422. Below the word line is an IPD layer 428, charge-trapping layers404, 414, 421, polysilicon layers 405, 415, 425, and tunneling layers409, 407, 408. Each charge-trapping layer 404, 414, 421 extendscontinuously in a respective NAND string. The flat configuration of thecontrol gate can be made thinner than a floating gate. Additionally, thememory cells can be placed closer together.

FIG. 4B illustrates a cross-sectional view of the structure of FIG. 4Aalong contact line connector 429. The NAND string 430 includes an SGStransistor 431, example memory cells 400, 433, . . . 435, and an SGDtransistor 436. Passageways in the IPD layer 428 in the SGS and SGDtransistors 431, 436 allow the control gate layers 402 and floating gatelayers to communicate. The control gate 402 and floating gate layers maybe polysilicon and the tunnel oxide layer may be silicon oxide, forinstance. The IPD layer 428 can be a stack of nitrides (N) and oxides(O) such as in a N-O-N-O-N configuration.

The NAND string may be formed on a substrate which comprises a p-typesubstrate region 455, an n-type well 456 and a p-type well 457. N-typesource/drain diffusion regions sd1, sd2, sd3, sd4, sd5, sd6 and sd7 areformed in the p-type well. A channel voltage, Vch, may be applieddirectly to the channel region of the substrate.

FIG. 5 illustrates an example block diagram of the sense block SB1 ofFIG. 1 . In one approach, a sense block comprises multiple sensecircuits. Each sense circuit is associated with data latches. Forexample, the example sense circuits 550 a, 551 a, 552 a, and 553 a areassociated with the data latches 550 b, 551 b, 552 b, and 553 b,respectively. In one approach, different subsets of bit lines can besensed using different respective sense blocks. This allows theprocessing load which is associated with the sense circuits to bedivided up and handled by a respective processor in each sense block.For example, a sense circuit controller 560 in SB1 can communicate withthe set of sense circuits and latches. The sense circuit controller 560may include a pre-charge circuit 561 which provides a voltage to eachsense circuit for setting a pre-charge voltage. In one possibleapproach, the voltage is provided to each sense circuit independently,e.g., via the data bus and a local bus. In another possible approach, acommon voltage is provided to each sense circuit concurrently. The sensecircuit controller 560 may also include a pre-charge circuit 561, amemory 562 and a processor 563. The memory 562 may store code which isexecutable by the processor to perform the functions described herein.These functions can include reading the latches 550 b, 551 b, 552 b, 553b which are associated with the sense circuits 550 a, 551 a, 552 a, 553a, setting bit values in the latches and providing voltages for settingpre-charge levels in sense nodes of the sense circuits 550 a, 551 a, 552a, 553 a. Further example details of the sense circuit controller 560and the sense circuits 550 a, 551 a, 552 a, 553 a are provided below.

In some embodiments, a memory cell may include a flag register thatincludes a set of latches storing flag bits. In some embodiments, aquantity of flag registers may correspond to a quantity of data states.In some embodiments, one or more flag registers may be used to control atype of verification technique used when verifying memory cells. In someembodiments, a flag bit's output may modify associated logic of thedevice, e.g., address decoding circuitry, such that a specified block ofcells is selected. A bulk operation (e.g., an erase operation, etc.) maybe carried out using the flags set in the flag register, or acombination of the flag register with the address register, as inimplied addressing, or alternatively by straight addressing with theaddress register alone.

FIG. 6A is a perspective view of a set of blocks 600 in an examplethree-dimensional configuration of the memory array 126 of FIG. 1 . Onthe substrate are example blocks BLK0, BLK1, BLK2, BLK3 of memory cells(storage elements) and a peripheral area 604 with circuitry for use bythe blocks BLK0, BLK1, BLK2, BLK3. For example, the circuitry caninclude voltage drivers 605 which can be connected to control gatelayers of the blocks BLK0, BLK1, BLK2, BLK3. In one approach, controlgate layers at a common height in the blocks BLK0, BLK1, BLK2, BLK3 arecommonly driven. The substrate 601 can also carry circuitry under theblocks BLK0, BLK1, BLK2, BLK3, along with one or more lower metal layerswhich are patterned in conductive paths to carry signals of thecircuitry. The blocks BLK0, BLK1, BLK2, BLK3 are formed in anintermediate region 602 of the memory device. In an upper region 603 ofthe memory device, one or more upper metal layers are patterned inconductive paths to carry signals of the circuitry. Each block BLK0,BLK1, BLK2, BLK3 comprises a stacked area of memory cells, wherealternating levels of the stack represent word lines. In one possibleapproach, each block BLK0, BLK1, BLK2, BLK3 has opposing tiered sidesfrom which vertical contacts extend upward to an upper metal layer toform connections to conductive paths. While four blocks BLK0, BLK1,BLK2, BLK3 are illustrated as an example, two or more blocks can beused, extending in the x- and/or y-directions.

In one possible approach, the length of the plane, in the x-direction,represents a direction in which signal paths to word lines extend in theone or more upper metal layers (a word line or SGD line direction), andthe width of the plane, in the y-direction, represents a direction inwhich signal paths to bit lines extend in the one or more upper metallayers (a bit line direction). The z-direction represents a height ofthe memory device.

FIG. 6B illustrates an example cross-sectional view of a portion of oneof the blocks BLK0, BLK1, BLK2, BLK3 of FIG. 6A. The block comprises astack 610 of alternating conductive and dielectric layers. In thisexample, the conductive layers comprise two SGD layers, two SGS layersand four dummy word line layers DWLD0, DWLD1, DWLS0 and DWLS1, inaddition to data word line layers (word lines) WLL0-WLL10. Thedielectric layers are labelled as DL0-DL19. Further, regions of thestack 610 which comprise NAND strings NS1 and NS2 are illustrated. EachNAND string encompasses a memory hole 618, 619 which is filled withmaterials which form memory cells adjacent to the word lines. A region622 of the stack 610 is shown in greater detail in FIG. 6D and isdiscussed in further detail below.

The 610 stack includes a substrate 611, an insulating film 612 on thesubstrate 611, and a portion of a source line SL. NS1 has a source-end613 at a bottom 614 of the stack and a drain-end 615 at a top 616 of thestack 610. Contact line connectors (e.g., slits, such as metal-filledslits) 617, 620 may be provided periodically across the stack 610 asinterconnects which extend through the stack 610, such as to connect thesource line to a particular contact line above the stack 610. Thecontact line connectors 617, 620 may be used during the formation of theword lines and subsequently filled with metal. A portion of a bit lineBL0 is also illustrated. A conductive via 621 connects the drain-end 615to BL0.

FIG. 6C illustrates a plot of memory hole diameter in the stack of FIG.6B. The vertical axis is aligned with the stack of FIG. 6B andillustrates a width (wMH), e.g., diameter, of the memory holes 618 and619. The word line layers WLL0-WLL10 of FIG. 6A are repeated as anexample and are at respective heights z0-z10 in the stack. In such amemory device, the memory holes which are etched through the stack havea very high aspect ratio. For example, a depth-to-diameter ratio ofabout 25-30 is common. The memory holes may have a circularcross-section. Due to the etching process, the memory hole width canvary along the length of the hole. Typically, the diameter becomesprogressively smaller from the top to the bottom of the memory hole.That is, the memory holes are tapered, narrowing at the bottom of thestack. In some cases, a slight narrowing occurs at the top of the holenear the select gate so that the diameter becomes slightly wider beforebecoming progressively smaller from the top to the bottom of the memoryhole.

Due to the non-uniformity in the width of the memory hole, theprogramming speed, including the program slope and erase speed of thememory cells can vary based on their position along the memory hole,e.g., based on their height in the stack. With a smaller diameter memoryhole, the electric field across the tunnel oxide is relatively stronger,so that the programming and erase speed is relatively higher. Oneapproach is to define groups of adjacent word lines for which the memoryhole diameter is similar, e.g., within a defined range of diameter, andto apply an optimized verify scheme for each word line in a group.Different groups can have different optimized verify schemes.

FIG. 6D illustrates a close-up view of the region 622 of the stack 610of FIG. 6B. Memory cells are formed at the different levels of the stackat the intersection of a word line layer and a memory hole. In thisexample, SGD transistors 680, 681 are provided above dummy memory cells682, 683 and a data memory cell MC. A number of layers can be depositedalong the sidewall (SW) of the memory hole 630 and/or within each wordline layer, e.g., using atomic layer deposition. For example, eachcolumn (e.g., the pillar which is formed by the materials within amemory hole 630) can include a charge-trapping layer or film 663 such asSiN or other nitride, a tunneling layer 664, a polysilicon body orchannel 665, and a dielectric core 666. A word line layer can include ablocking oxide/block high-k material 660, a metal barrier 661, and aconductive metal 662 such as Tungsten as a control gate. For example,control gates 690, 691, 692, 693, and 694 are provided. In this example,all of the layers except the metal are provided in the memory hole 630.In other approaches, some of the layers can be in the control gatelayer. Additional pillars are similarly formed in the different memoryholes. A pillar can form a columnar active area (AA) of a NAND string.

When a data memory cell MC is programmed, electrons are stored in aportion of the charge-trapping layer 663 which is associated with thememory cell MC. These electrons are drawn into the charge-trapping layer663 from the channel 665, and through the tunneling layer 664. The Vthof a memory cell MC is increased in proportion to the amount of storedcharge. During an erase operation, the electrons return to the channel665.

Each of the memory holes 630 can be filled with a plurality of annularlayers comprising a blocking oxide layer, a charge-trapping layer 663, atunneling layer 664 and a channel layer 665. A core region of each ofthe memory holes 630 is filled with a body material, and the pluralityof annular layers are between the core region and the word line in eachof the memory holes 630.

The NAND string can be considered to have a floating body channel 665because the length of the channel 665 is not formed on a substrate.Further, the NAND string is provided by a plurality of word line layersabove one another in a stack, and separated from one another bydielectric layers.

FIG. 7A shows a schematic plan view of a memory array 700 with aplurality of memory holes 722, which can be vertical memory cell strandsas described herein, and a plurality of dummy holes 705, which need notone complete memory structures. A shallow trench etch or shallow etchingfeature (SHE) 710 extends through a plurality of word lines (forexample, five) but not fully through the chip to electrically isolateadjacent strings from one another. The SHE extends directly through agroup of aligned dummy holes 705, thereby preventing those dummy holes705 from storing data or otherwise being functional memory cells.

Referring now to FIGS. 8A and 8B, there are no dummy holes. Unlike thememory structure 700 of FIGS. 7A and 7B, the SHE 810 is located in a gapbetween two adjacent rows of memory cells 825 and overlaps with memoryholes 825, thereby creating a working strand that has a trench etcheddown into a side of at least the SGD switch at the top of the workingmemory strand, here shown as memory holes 825. This configurationsubstantially improves yield and memory density as all of the memoryholes 822, 825 are functional, i.e., fewer memory holes are wasted.

Unlike the fully circular memory holes 822, the memory holes 825 and theSGD switches that are partially cut by the SHE 810 have a semi-circularshape, which can either be a half circle or can be more or less than ahalf-circle. In some cases, the memory holes 825 and SGD switches can beless than half circles on one side of the SHE 810 and more than halfcircles on the other side of the SHE 810.

The memory holes 822, 825 are connected with a plurality of bit lines830 (labeled as bit lines 0-7 in FIG. 8A). For ease of illustration,only eight bit lines 830 have been shown. The bit lines 830 extend overabove the memory holes and are connected to select memory holes viaconnection points. The memory holes in each string area also connectedat one end to an SGD switch and at the other end to an SGS switch.

At the end of a successful programming process (with verification), thethreshold voltages of the memory cells should be within one or moredistributions of threshold voltages for programmed memory cells orwithin a distribution of threshold voltages for erased memory cells, asappropriate. FIG. 9 illustrates example threshold voltage Vtdistributions corresponding to data states for the memory cell arraywhen each memory cell stores three bits of data. Other embodiment,however, may use more or fewer than three bits of data per memory cell.FIG. 9 shows eight threshold voltage Vt distributions corresponding toan Erase state and programmed states A-G. In one embodiment, thethreshold voltages in the Erase state are negative and the thresholdvoltages in the programmed states A-G are positive.

However, the threshold voltages in one or more of programmed states A-Gmay be negative. Thus, in one embodiment, at least VrA is negative.Other voltages such as VvA, VrB, VvB, etc., may also be negative.

Between each of the data states are read reference voltages used forreading data from memory cells. For example, FIG. 9 shows read referencevoltage VrA between the erase state and the A-state, and VrB between theA-state and B-state. By testing whether the threshold voltage of a givenmemory cell is above or below the respective read reference voltages,the system can determine what state the memory cell is in.

At or near the lower edge of each programmed state are verify referencevoltages. For example, FIG. 9 shows VvA for the A-state and VvB for theB-state. When programming memory cells to a given state, the system willtest whether those memory cells have a threshold voltage greater than orequal to the verify reference voltage.

As discussed above and referring back to FIGS. 8A and 8B, the SHE trench810 may be etched into a portion of the drain-side select gate SGDswitch. Ideally the SHE cut or trench 810 is needed only down to thedrain-side select gate SGD layer (i.e., SGD1 in FIG. 6D). However, dueto process (etching) variation, it may be extremely difficult toconsistently and precisely cut to the drain-side select gate SGD layer,some dies will be cut to a first dummy word line or layer DD0 (i.e.,DWLD0 in FIG. 6D) and some even cut to a second dummy word line or layerDD1 (i.e., DWLD1 in FIG. 6D). When the SHE cut or trench 810 is closerto the data word lines (i.e., deeper), data retention becomessignificantly worse. This is due to SHE etching/clean induced physicaldamage of memory cells close to the physical SHE bottom. FIG. 10 shows across-sectional top view of memory holes (MHs) (shaded circles in FIG.10 ) taken at a drain-side select gate SGD layer (leftmost portion ofFIG. 10 ) and an edge word line layer (rightmost portion of FIG. 10 ).Rows of memory holes having semi-circle drain-side select gates SC-SGDare indicated with dashed boxes, while the other memory holes do notinclude semi-circle drain-side select gates SC-SGD. FIG. 11 showsthreshold voltage distributions and corresponding data or memory statesbefore (plot indicated as 850) and after high temperature data retention(HTDR) testing (plot indicated as 852) for an example memory apparatus.As shown, memory cells of memory holes without semi-circle drain-sideselect gates SC-SGD (i.e., full-circle drain-side select gates FC-SGD)and associated with the edge word line exhibit comparatively better dataretention and the memory cells of memory holes with semi-circledrain-side select gates SC-SGD and associated with the edge word lineexhibit comparatively worse data retention. In other words, the memorycells of memory holes with semi-circle drain-side select gates SC-SGDlose more charge than memory cells of memory holes without semi-circledrain-side select gates SC-SGD due to the additional SHE RIE damage, butonly for the edge word line.

One solution to the data retention issues resulting from the depth ofthe SHE trench 810 is to have one or more additional dummy word linelayers to avoid this edge word line data retention loss. However, suchan additional dummy word line increases process cost. Another solutionis to introduce plasma induced oxidation (PIO) process to recover RIEdamage. This has been proven effective to mitigate the edge word linedata retention issues, nevertheless, it is not a complete fix as somestates (e.g., F/G-state) may still be contaminated in the best case.

Consequently, described herein is a memory apparatus (e.g., memorydevice 100 of FIG. 1A) including memory cells (e.g., data memory cell MCand dummy memory cells 682, 683 of FIG. 6D) connected to one of aplurality of word lines (e.g., data word line layers (word lines)WLL0-WLL10 of FIG. 6B or WLL10 of FIG. 6D) including at least one edgeword line and a plurality of other data word lines. The memory cells arearranged in strings (e.g., NAND strings NS1 and NS2 of FIG. 6B) andconfigured to retain a threshold voltage Vt or Vth corresponding to oneof a plurality of data states (e.g., see FIG. 9 ). The apparatus alsoincludes a control circuit or means (e.g., one or any combination ofcontrol circuitry 110, decoders 114/132, power control module 116, senseblocks SBb, SB2, . . . , SBp, read/write circuits 128, controller 122 ofFIG. 1A, control circuit 150 of FIG. 1B, and/or sense circuit controller560 of FIG. 5 and so forth) coupled to the plurality of word lines andthe strings. The control means is configured to identify the at leastone edge word line. The control means is also configured to periodicallyapply a program voltage to the at least one edge word line to reprogramthe memory cells associated with the at least one edge word line withouterasing the memory cells associated with the at least one edge wordline.

Referring back to FIG. 6B, for example, the plurality of word lines(e.g., word line layers (word lines) WLL0-WLL10 of FIG. 6B) and aplurality of dielectric layers (e.g., DL0-DL19 of FIG. 6B) extendhorizontally and overlay one another in an alternating fashion in astack (e.g., stack 610) and the strings (e.g., NAND strings NS1 and NS2of FIG. 6B) extend vertically through the stack. The memory cells areconnected in series between at least one drain-side select gate SGDtransistor on a drain-side of each of the strings and at least onesource-side select gate transistor on a source-side of each of thestrings. The at least one drain-side select gate SGD transistor isconnected to one of a plurality of bit lines (e.g., BL0 of FIG. 6B) andthe at least one source-side select gate transistor is connected to asource line. Damage of memory cells close to the bottom of the SHEtrench 810 (FIGS. 8B, 10, and 11 ) and resulting data retention issuesusually penetrates about one or two word lines deeper than a bottom ofthe SHE trench 810. Fortunately, this data retention issue primarilyonly happens on the at least one edge word line. So, according to anaspect, the at least one edge word line (e.g., WLL10 of FIG. 6B) isdisposed vertically above the plurality of other data word lines (e.g.,data word line layers (word lines) WLL0-WLL9 of FIG. 6B) and immediatelyadjacent the at least one drain-side select gate SGD transistor (e.g.,681 of FIG. 6D).

According to an aspect, the control means is further configured to storedata stored information identifying which of the plurality of word linesare the at least one edge word line and the plurality of other data wordlines. The control means may also store edge information identifyingwhich of the memory cells connected to the plurality of word linescontain the data. Accordingly, the control means can then utilize thedata stored information and the edge information to determine whethereach of the plurality of word lines of the one of the plurality ofblocks is the at least one edge word line and whether the memory cellsconnected to the at least one edge word line contain the data.

FIG. 12 shows another cross-sectional top view of memory holes (MHs)(shaded circles in FIG. 12 ) taken at the drain-side select gate SGDlayer (leftmost portion of FIG. 12 ), a layer corresponding to one ofthe plurality of other data word lines (middle portion of FIG. 12 ), andthe edge word line layer (rightmost portion of FIG. 12 ). As shown, thememory holes or strings are arranged in rows including full circle rowsand semi-circle rows. The semi-circle rows comprise memory holes formingthe strings being partially cut by a SHE trench extending verticallyinto the stack. So, the semi-circle rows of strings have semi-circledrain-side select gates SC-SGD and are shown aligned with the SHEtrenches 810 and indicated with dashed boxes, while full-circle rows ofthe other memory holes do not include semi-circle drain-side selectgates SC-SGD and are indicated with separate dashed boxes. If it isdesired to reduce system power or current consumption, only semi-circlerows may be refreshed. Thus, according to an aspect, the control meansis further configured to apply an inhibiting bit line voltage to ones ofthe plurality of bit lines coupled to the strings of the full circlerows (indicated as No Refresh or refresh in FIG. 12 ) whilereprogramming the memory cells associated with the at least one edgeword line to discourage reprogramming of the memory cells in the stringsassociated with the full circle rows. The control means is alsoconfigured to simultaneously apply a select bit line voltage (e.g.,approximately 0 volts) to ones of the plurality of bit lines coupled tothe strings of the semi-circle rows while reprogramming the memory cellsassociated with the at least one edge word line to encouragereprogramming of the memory cells in the strings associated with thesemi-circle rows (indicated as Refresh in FIG. 12 ). Nevertheless, bothfull-circle and semi-circle memory hole rows may be refreshed together,so it should be understood that the memory cells in the stringsassociated with the full circle rows may instead be refreshed at thesame time as memory cells in the strings associated with the semi-circlerows (i.e., all of the memory cells connected to the at least one edgeword line).

As discussed above, the memory apparatus can further include the errorcorrection code engine 245 (FIG. 1A) configured to determine and correcterrors in reading the memory cells. In addition, referring back to FIG.9 , the threshold voltage Vt possible for each of the memory cells spansa threshold window 900. Each of the memory cells is configured to storea plurality of bits. The plurality of data states includes an erasedstate (e.g., Erase state in FIG. 9 ) at a first end 902 of the thresholdwindow 900 and a plurality of programmed data states (e.g., states A, B,C, D, E, F, and G of FIG. 9 ) each corresponding to the thresholdvoltage Vt being higher than the threshold voltage Vt associated withthe erased state. The plurality of programmed data states includes ahighest data state (e.g., state G of FIG. 9 ) at a second end 904 of thethreshold window opposite the first end 902 and associated with thethreshold voltage Vt being higher than the threshold voltage Vtassociated with the erased state and at least one other of the pluralityof programmed data states. Therefore, according to additional aspects,the control means is further configured to count an edge higher datastate quantity of the memory cells associated with the at least one edgeword line having the threshold voltage Vt above a verify voltage (e.g.,VvG in FIG. 9 ) corresponding to the highest data state (e.g., state Gof FIG. 9 ). The control means is also configured to determine whetherthe edge higher data state quantity is less than an edge highest datastate threshold. The control means is additionally configured to readdata of the memory cells associated with the at least one edge word lineand generate corrected data from the data using the error correctioncode engine 245 in response to determining the edge higher data statequantity is less than an edge highest data state threshold. In addition,the control means uses the corrected data while reprogramming the memorycells associated with the at least one edge word line without erasingthe memory cells associated with the at least one edge word line.

According to an aspect, the memory cells comprise a plurality of blocks.So, the control means is further configured to determine whether all ofthe plurality of blocks have been checked for the at least one edge wordline in response to a proactive refresh operation being triggered. Forexample, the control means can determine when approximately a few monthsto ˜1 year have elapsed to trigger the proactive refresh orreprogramming. The control means is also configured to end reprogrammingthe memory cells associated with the at least one edge word line withouterasing the memory cells associated with the at least one edge word linein response to determining all of the plurality of blocks have beenchecked for the at least one edge word line. The control means proceedsto check one of the plurality of blocks for the at least one edge wordline in response to determining not all of the plurality of blocks havebeen checked for the at least one edge word line. The control means isalso configured to determine whether each of the plurality of word linesof the one of the plurality of blocks is the at least one edge word lineand whether the memory cells connected to the at least one edge wordline contain the data. The control means returns to determine whetherall of the plurality of blocks have been checked for the at least oneedge word line in response to determining at least one of the each ofthe plurality of word lines of the one of the plurality of blocks is notthe at least one edge word line and the memory cells connected to the atleast one edge word line does not contain the data. In addition, thecontrol means returns to determine whether all of the plurality ofblocks have been checked for the at least one edge word line in responseto determining the edge higher data state quantity is not less than anedge higher data state threshold. The control means is additionallyconfigured to return to determine whether all of the plurality of blockshave been checked for the at least one edge word line followingreprogramming the memory cells associated with the at least one edgeword line without erasing the memory cells associated with the at leastone edge word line.

According to an aspect, the plurality of data states includes a totalstate quantity of the plurality of data states and the edge highest datastate threshold is equal to one over the total state quantity of theplurality of data states multiplied by an overall cell quantity of allof the memory cells. For example, referring back to FIG. 9 , theplurality of bits includes three bits (i.e., triple level cell (TLC)),meaning the total state quantity of the plurality of data states iseight. So, the plurality of programmed data states can include, in orderof the threshold voltage Vt increasing in magnitude, a first data stateA and a second data state B and a third data state C and a fourth datastate D and a fifth data state E and a sixth data state F and a seventhdata state G. Thus, the highest data state is the seventh data state Gand the edge highest data state threshold is equal to one over eightmultiplied by the overall cell quantity of all of the memory cells.

FIG. 13 shows the plurality of bit lines BLs connecting to memory holesor strings in a top representation 946 and perspective representation948 having full-circle (FC) and semi-circle (SC) drain-side select gatesSGD and threshold voltage Vt distributions 950, 952, 954, 956 for memorycells in the strings or memory holes associated with the semi-circlerows and full-circle rows. The threshold voltage Vt distributions 950,952, 954, 956 are shown after programming, after high temperature dataretention testing, determining the edge higher data state quantitygreater less than an edge highest data state threshold (e.g., too muchdownshift of state G memory cells), and after reprogramming the memorycells associated with the at least one edge word line without erasingthe memory cells associated with the at least one edge word line (i.e.,reprogramming without erase). As shown, right after the programoperation (threshold voltage Vt distribution of FIG. 13 labeled 950),all of the data or memory states are formed properly. Then, after hightemperature data retention testing (i.e., after baking or a long periodof time)(threshold voltage Vt distribution of FIG. 13 labeled 952),memory cells associated with memory holes in semi-circle SGD rowsexhibit more aggressive downshift compared to memory cells associatedwith memory holes in full-circle SGD rows. Now, whether there issignificant downshift or not can be detected (e.g., by determiningwhether the edge higher data state quantity is less than the edgehighest data state threshold) (threshold voltage Vt distribution of FIG.13 labeled 954). It is possible to leave a sufficient margin before trueECC failures, thus data may be readout correctly using the ECC engine245 (data reconstruction). After data reconstruction, the memory cellsassociated with the at least one edge word line (e.g., top edge wordline, labeled edge data WL in the perspective representation 948) may bereprogrammed without erasing the memory cells associated with the atleast one edge word line (threshold voltage Vt distribution of FIG. 13labeled 956). Therefore, data is fully recovered.

Referring now to FIG. 14 , a method of operating a memory apparatus isalso provided. As discussed above, the memory apparatus (e.g., memorydevice 100 of FIG. 1A) includes including memory cells (e.g., datamemory cell MC and dummy memory cells 682, 683 of FIG. 6D) connected toone of a plurality of word lines including at least one edge word line(e.g., WLL10 of FIG. 6B) and a plurality of other data word lines (e.g.,data word line layers (word lines) WLL0-WLL9 of FIG. 6B). The memorycells are arranged in strings (e.g., NAND strings NS1 and NS2 of FIG.6B) and configured to retain a threshold voltage Vt or Vth correspondingto one of a plurality of data states (e.g., see FIG. 9 ). The methodincludes the step of 1000 triggering a proactive refresh. The methodalso includes the step of 1002 identifying the at least one edge wordline. The method also includes the step of 1004 periodically applying aprogram voltage to the at least one edge word line to reprogram thememory cells associated with the at least one edge word line withouterasing the memory cells associated with the at least one edge wordline. So, again, the plurality of word lines and a plurality ofdielectric layers extend horizontally and overlay one another in analternating fashion in a stack, the strings extend vertically throughthe stack, the memory cells connected in series between at least onedrain-side select gate SGD transistor on a drain-side of each of thestrings and connected to one of a plurality of bit lines and at leastone source-side select gate transistor on a source-side of each of thestrings and connected to a source line, the at least one edge word linebeing disposed vertically above the plurality of other data word linesand immediately adjacent the at least one drain-side select gate SGDtransistor.

As discussed, the memory cells comprise a plurality of blocks, so inmore detail, the method proceeds by 1006 determining whether all of theplurality of blocks have been checked for the at least one edge wordline in response to a proactive refresh operation being triggered. Themethod then includes the step of 1008 ending reprogramming the memorycells associated with the at least one edge word line without erasingthe memory cells associated with the at least one edge word line inresponse to determining all of the plurality of blocks have been checkedfor the at least one edge word line. The method continues by 1010proceeding to check one of the plurality of blocks for the at least oneedge word line in response to determining not all of the plurality ofblocks have been checked for the at least one edge word line.

The method additionally includes the step of 1012 determining whethereach of the plurality of word lines of the one of the plurality ofblocks is the at least one edge word line and whether the memory cellsconnected to the at least one edge word line contain the data. Accordingto an aspect, and as discussed above, information related to whetherones of the plurality of word lines are the at least one edge word lineand whether the corresponding memory cells contain data may be storedand/or tracked by the control means, for example. Thus, the methodfurther includes the step of storing data stored information identifyingwhich of the plurality of word lines are the at least one edge word lineand the plurality of other data word lines. The method also can includethe step of storing edge information identifying which of the memorycells connected to the plurality of word lines contain the data. Suchsteps could, for instance be carried out during erasing, programming,and/or reading operations of the memory apparatus. The method continueswith the step of 1014 utilizing the data stored information and the edgeinformation when determining whether each of the plurality of word linesof the one of the plurality of blocks is the at least one edge word lineand whether the memory cells connected to the at least one edge wordline contain the data. The method also includes the step of 1016returning to 1006 determining whether all of the plurality of blockshave been checked for the at least one edge word line in response todetermining at least one of the each of the plurality of word lines ofthe one of the plurality of blocks is not the at least one edge wordline and the memory cells connected to the at least one edge word linedoes not contain the data.

As discussed above, the memory apparatus further includes the errorcorrection code engine 245 configured to determine and correct errors inreading the memory cells. In addition, referring back to FIG. 9 , thethreshold voltage Vt possible for each of the memory cells spans athreshold window 900. Each of the memory cells is configured to store aplurality of bits. The plurality of data states includes an erased state(e.g., Erase state in FIG. 9 ) at a first end 902 of the thresholdwindow 900 and a plurality of programmed data states (e.g., states A, B,C, D, E, F, and G of FIG. 9 ) each corresponding to the thresholdvoltage Vt being higher than the threshold voltage Vt associated withthe erased state. The plurality of programmed data states includes ahighest data state (e.g., state G of FIG. 9 ) at a second end 904 of thethreshold window opposite the first end 902 and associated with thethreshold voltage Vt being higher than the threshold voltage Vtassociated with the erased state and at least one other of the pluralityof programmed data states. So, the method further includes the step of1018 counting an edge higher data state quantity of the memory cellsassociated with the at least one edge word line having the thresholdvoltage Vt above a verify voltage (e.g., VvG in FIG. 9 ) correspondingto the highest data state (e.g., state G of FIG. 9 ). Next, 1020determining whether the edge higher data state quantity is less than anedge highest data state threshold.

Again, according to an aspect, the plurality of data states includes atotal state quantity of the plurality of data states and the edgehighest data state threshold is equal to one over the total statequantity of the plurality of data states multiplied by an overall cellquantity of all of the memory cells. For instance, referring back toFIG. 9 , the plurality of bits includes three bits (i.e., triple levelcell (TLC)), meaning the total state quantity of the plurality of datastates is eight. So, the plurality of programmed data states caninclude, in order of the threshold voltage Vt increasing in magnitude, afirst data state A and a second data state B and a third data state Cand a fourth data state D and a fifth data state E and a sixth datastate F and a seventh data state G. Thus, the highest data state is theseventh data state G and the edge highest data state threshold is equalto one over eight multiplied by the overall cell quantity of all of thememory cells. The method also includes the step of 1022 returning to1006 determining whether all of the plurality of blocks have beenchecked for the at least one edge word line in response to determiningthe edge higher data state quantity is not less than an edge higher datastate threshold.

The next step of the method is 1024 reading data of the memory cellsassociated with the at least one edge word line (e.g., lower page (LP,middle page (MP), and upper page (UP)) and generating corrected datafrom the data using the error correction code engine 245 in response todetermining the edge higher data state quantity is less than an edgehighest data state threshold. In more detail, the method includes thestep of 1026 using the corrected data while reprogramming the memorycells associated with the at least one edge word line without erasingthe memory cells associated with the at least one edge word line. Asdiscussed, the strings are arranged in rows including full circle rowsand semi-circle rows comprising memory holes forming the strings beingpartially cut by a shallow hole etch extending vertically into thestack. Thus, according to an aspect, the method can further include thestep of 1028 applying an inhibiting bit line voltage to ones of theplurality of bit lines coupled to the strings of the full circle rowswhile reprogramming the memory cells associated with the at least oneedge word line to discourage reprogramming of the memory cells in thestrings associated with the full circle rows. In addition, the methodcan include the step of 1030 simultaneously applying a select bit linevoltage (e.g., approximately 0 volts) to ones of the plurality of bitlines coupled to the strings of the semi-circle rows while reprogrammingthe memory cells associated with the at least one edge word line toencourage reprogramming of the memory cells in the strings associatedwith the semi-circle rows. The method then includes the step of 1030returning to 1006 determining whether all of the plurality of blockshave been checked for the at least one edge word line followingreprogramming the memory cells associated with the at least one edgeword line without erasing the memory cells associated with the at leastone edge word line.

The advantages of the memory apparatus and method disclosed hereininclude no reliability concerns as refresh or reprogramming does notrequire any erase operation and only memory cells associated with the atleast one edge word line are reprogrammed. The downshifted memory cells(in the at least one edge word line) are reprogrammed back to normalwith small threshold voltage Vt swing. Furthermore, because the only theat least one edge word line (e.g., top edge WL), reprogramming does nothave any “precharge” issues, so the memory cells easily be programmedback without precharge/boosting issues. While other solutions such asPIO processes greatly improve high temperature data retention of the atleast one edge word line, further improvement is possible, however,combined with PIO processes, very frequent refresh or programming is notrequired (e.g., approximately a few months to ˜1 year per refresh).Thus, OPS (on-pitch SGD) technology becomes more viable and no extradummy word lines are needed (thus, process/die cost can be reduced).

Clearly, changes may be made to what is described and illustrated hereinwithout, however, departing from the scope defined in the accompanyingclaims. The foregoing description of the embodiments has been providedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

What is claimed is:
 1. A memory apparatus, comprising: memory cellsconnected to one of a plurality of word lines including at least oneedge word line and a plurality of other data word lines and arranged instrings and configured to retain a threshold voltage corresponding toone of a plurality of data states, wherein the strings are arranged inrows including full circle rows and semi-circle rows; and a controlmeans coupled to the plurality of word lines and the strings andconfigured to: identify the at least one edge word line, andperiodically apply a program voltage to the at least one edge word lineto reprogram the memory cells associated with the at least one edge wordline without erasing the memory cells associated with the at least oneedge word line, wherein periodically applying the program voltageincludes applying an inhibiting bit line voltage to ones of a pluralityof bit lines coupled to the strings of the full circle rows whilereprogramming the memory cells associated with the at least one edgeword line to inhibit reprogramming of the memory cells in the stringsassociated with the full circle rows.
 2. The memory apparatus as setforth in claim 1, wherein the plurality of word lines and a plurality ofdielectric layers extend horizontally and overlay one another in analternating fashion in a stack, the strings extend vertically throughthe stack, the memory cells connected in series between at least onedrain-side select gate transistor on a drain-side of each of the stringsand connected to one of the plurality of bit lines and at least onesource-side select gate transistor on a source-side of each of thestrings and connected to a source line, the at least one edge word linebeing disposed vertically above the plurality of other data word lines,wherein, among the plurality of word lines, the at least one edge wordline is nearest to the at least one drain-side select gate transistor.3. The memory apparatus as set forth in claim 2, the semi-circle rowscomprising memory holes forming the strings being partially cut by ashallow hole etch extending vertically into the stack and wherein, toperiodically apply the program voltage, the control means is furtherconfigured to: simultaneously apply a select bit line voltage to ones ofthe plurality of bit lines coupled to the strings of the semi-circlerows while reprogramming the memory cells associated with the at leastone edge word line to encourage reprogramming of the memory cells in thestrings associated with the semi-circle rows.
 4. The memory apparatus asset forth in claim 1, further including an error correction code engineconfigured to determine and correct errors in reading the memory cellsand wherein the threshold voltage possible for each of the memory cellsspans a threshold window, each of the memory cells is configured tostore a plurality of bits, the plurality of data states includes anerased state at a first end of the threshold window and a plurality ofprogrammed data states each corresponding to the threshold voltage beinghigher than the threshold voltage associated with the erased state, theplurality of programmed data states including a highest data state at asecond end of the threshold window opposite the first end and associatedwith the threshold voltage being higher than the threshold voltageassociated with the erased state and at least one other of the pluralityof programmed data states and the control means is further configuredto: count an edge higher data state quantity of the memory cellsassociated with the at least one edge word line having the thresholdvoltage above a verify voltage corresponding to the highest data state;determine whether the edge higher data state quantity is less than anedge highest data state threshold; read data of the memory cellsassociated with the at least one edge word line and generate correcteddata from the data using the error correction code engine in response todetermining the edge higher data state quantity is less than the edgehighest data state threshold; and use the corrected data whilereprogramming the memory cells associated with the at least one edgeword line without erasing the memory cells associated with the at leastone edge word line.
 5. The memory apparatus as set forth in claim 4,wherein the memory cells comprise a plurality of blocks and the controlmeans is further configured to: determine whether all of the pluralityof blocks have been checked for the at least one edge word line inresponse to a proactive refresh operation being triggered; endreprogramming the memory cells associated with the at least one edgeword line without erasing the memory cells associated with the at leastone edge word line in response to determining all of the plurality ofblocks have been checked for the at least one edge word line; proceed tocheck one of the plurality of blocks for the at least one edge word linein response to determining not all of the plurality of blocks have beenchecked for the at least one edge word line; determine whether each ofthe plurality of word lines of the one of the plurality of blocks is theat least one edge word line and whether the memory cells connected tothe at least one edge word line contain the data; return to determinewhether all of the plurality of blocks have been checked for the atleast one edge word line in response to determining at least one of theeach of the plurality of word lines of the one of the plurality ofblocks is not the at least one edge word line and the memory cellsconnected to the at least one edge word line does not contain the data;return to determine whether all of the plurality of blocks have beenchecked for the at least one edge word line in response to determiningthe edge higher data state quantity is not less than an edge higher datastate threshold; and return to determine whether all of the plurality ofblocks have been checked for the at least one edge word line followingreprogramming the memory cells associated with the at least one edgeword line without erasing the memory cells associated with the at leastone edge word line.
 6. The memory apparatus as set forth in claim 5,wherein the control means is further configured to: store data storedinformation identifying which of the plurality of word lines are the atleast one edge word line and the plurality of other data word lines;store edge information identifying which of the memory cells connectedto the plurality of word lines contain the data; and utilize the datastored information and the edge information to determine whether each ofthe plurality of word lines of the one of the plurality of blocks is theat least one edge word line and whether the memory cells connected tothe at least one edge word line contain the data.
 7. The memoryapparatus as set forth in claim 4, wherein the plurality of data statesincludes a total state quantity of the plurality of data states.
 8. Thememory apparatus as set forth in claim 7, wherein the plurality of bitsincludes three bits, the total state quantity of the plurality of datastates is eight, the plurality of programmed data states includes, inorder of the threshold voltage increasing in magnitude, a first datastate and a second data state and a third data state and a fourth datastate and a fifth data state and a sixth data state and a seventh datastate, and the highest data state is the seventh data state.
 9. Acontroller in communication with a memory apparatus including memorycells connected to one of a plurality of word lines including at leastone edge word line and a plurality of other data word lines and arrangedin strings and configured to retain a threshold voltage corresponding toone of a plurality of data states, wherein the strings are arranged inrows including full circle rows and semi-circle rows, the controllerconfigured to: identify the at least one edge word line; and instructthe memory apparatus to periodically apply a program voltage to the atleast one edge word line to reprogram the memory cells associated withthe at least one edge word line without erasing the memory cellsassociated with the at least one edge word line, wherein periodicallyapplying the program voltage includes applying an inhibiting bit linevoltage to ones of a plurality of bit lines coupled to the strings ofthe full circle rows while reprogramming the memory cells associatedwith the at least one edge word line to inhibit reprogramming of thememory cells in the strings associated with the full circle rows. 10.The controller as set forth in claim 9, wherein the plurality of wordlines and a plurality of dielectric layers extend horizontally andoverlay one another in an alternating fashion in a stack, the stringsextend vertically through the stack, the memory cells connected inseries between at least one drain-side select gate transistor on adrain-side of each of the strings and connected to one of the pluralityof bit lines and at least one source-side select gate transistor on asource-side of each of the strings and connected to a source line, theat least one edge word line being disposed vertically above theplurality of other data word lines, wherein, among the plurality of wordlines, the at least one edge word line is nearest to the at least onedrain-side select gate transistor.
 11. The controller as set forth inclaim 10, the semi-circle rows comprising memory holes forming thestrings being partially cut by a shallow hole etch extending verticallyinto the stack, wherein, to periodically apply the program voltage, thecontroller is further configured to: instruct the memory apparatus tosimultaneously apply a select bit line voltage to ones of the pluralityof bit lines coupled to the strings of the semi-circle rows whilereprogramming the memory cells associated with the at least one edgeword line to encourage reprogramming of the memory cells in the stringsassociated with the semi-circle rows.
 12. The controller as set forth inclaim 9, wherein at least one of the memory apparatus and the controllerfurther includes an error correction code engine configured to determineand correct errors in reading the memory cells and wherein the thresholdvoltage possible for each of the memory cells spans a threshold window,each of the memory cells is configured to store a plurality of bits, theplurality of data states includes an erased state at a first end of thethreshold window and a plurality of programmed data states eachcorresponding to the threshold voltage being higher than the thresholdvoltage associated with the erased state, the plurality of programmeddata states including a highest data state at a second end of thethreshold window opposite the first end and associated with thethreshold voltage being higher than the threshold voltage associatedwith the erased state and at least one other of the plurality ofprogrammed data states, the controller further configured to: instructthe memory apparatus to count an edge higher data state quantity of thememory cells associated with the at least one edge word line having thethreshold voltage above a verify voltage corresponding to the highestdata state; determine whether the edge higher data state quantity isless than an edge highest data state threshold; instruct the memoryapparatus to read data of the memory cells associated with the at leastone edge word line and generate corrected data from the data using theerror correction code engine in response to determining the edge higherdata state quantity is less than the edge highest data state threshold;and instruct the memory apparatus to use the corrected data whilereprogramming the memory cells associated with the at least one edgeword line without erasing the memory cells associated with the at leastone edge word line.
 13. The controller as set forth in claim 12, whereinthe memory cells comprise a plurality of blocks, the controller furtherconfigured to: determine whether all of the plurality of blocks havebeen checked for the at least one edge word line in response to aproactive refresh operation being triggered; instruct the memoryapparatus to end reprogramming the memory cells associated with the atleast one edge word line without erasing the memory cells associatedwith the at least one edge word line in response to determining all ofthe plurality of blocks have been checked for the at least one edge wordline; instruct the memory apparatus to proceed to check one of theplurality of blocks for the at least one edge word line in response todetermining not all of the plurality of blocks have been checked for theat least one edge word line; determine whether each of the plurality ofword lines of the one of the plurality of blocks is the at least oneedge word line and whether the memory cells connected to the at leastone edge word line contain the data; return to determine whether all ofthe plurality of blocks have been checked for the at least one edge wordline in response to determining at least one of the each of theplurality of word lines of the one of the plurality of blocks is not theat least one edge word line and the memory cells connected to the atleast one edge word line does not contain the data; return to determinewhether all of the plurality of blocks have been checked for the atleast one edge word line in response to determining the edge higher datastate quantity is not less than an edge higher data state threshold; andreturn to determine whether all of the plurality of blocks have beenchecked for the at least one edge word line following reprogramming thememory cells associated with the at least one edge word line withouterasing the memory cells associated with the at least one edge wordline.
 14. A method of operating a memory apparatus including memorycells connected to one of a plurality of word lines including at leastone edge word line and a plurality of other data word lines and arrangedin strings and configured to retain a threshold voltage corresponding toone of a plurality of data states, wherein the strings are arranged inrows including full circle rows and semi-circle rows, the methodcomprising the steps of: identifying the at least one edge word line;and periodically applying a program voltage to the at least one edgeword line to reprogram the memory cells associated with the at least oneedge word line without erasing the memory cells associated with the atleast one edge word line, wherein periodically applying the programvoltage includes applying an inhibiting bit line voltage to ones of aplurality of bit lines coupled to the strings of the full circle rowswhile reprogramming the memory cells associated with the at least oneedge word line to inhibit reprogramming of the memory cells in thestrings associated with the full circle rows.
 15. The method as setforth in claim 14, wherein the plurality of word lines and a pluralityof dielectric layers extend horizontally and overlay one another in analternating fashion in a stack, the strings extend vertically throughthe stack, the memory cells connected in series between at least onedrain-side select gate transistor on a drain-side of each of the stringsand connected to one of the plurality of bit lines and at least onesource-side select gate transistor on a source-side of each of thestrings and connected to a source line, the at least one edge word linebeing disposed vertically above the plurality of other data word lines,wherein, among the plurality of word lines, the at least one edge wordline is nearest to the at least one drain-side select gate transistor.16. The method as set forth in claim 15, the semi-circle rows comprisingmemory holes forming the strings being partially cut by a shallow holeetch extending vertically into the stack, the method further including,to periodically apply the program voltage: simultaneously applying aselect bit line voltage to ones of the plurality of bit lines coupled tothe strings of the semi-circle rows while reprogramming the memory cellsassociated with the at least one edge word line to encouragereprogramming of the memory cells in the strings associated with thesemi-circle rows.
 17. The method as set forth in claim 14, wherein thememory apparatus further includes an error correction code engineconfigured to determine and correct errors in reading the memory cellsand wherein the threshold voltage possible for each of the memory cellsspans a threshold window, each of the memory cells is configured tostore a plurality of bits, the plurality of data states includes anerased state at a first end of the threshold window and a plurality ofprogrammed data states each corresponding to the threshold voltage beinghigher than the threshold voltage associated with the erased state, theplurality of programmed data states including a highest data state at asecond end of the threshold window opposite the first end and associatedwith the threshold voltage being higher than the threshold voltageassociated with the erased state and at least one other of the pluralityof programmed data states, the method further including the steps of:counting an edge higher data state quantity of the memory cellsassociated with the at least one edge word line having the thresholdvoltage above a verify voltage corresponding to the highest data state;determining whether the edge higher data state quantity is less than anedge highest data state threshold; reading data of the memory cellsassociated with the at least one edge word line and generating correcteddata from the data using the error correction code engine in response todetermining the edge higher data state quantity is less than the edgehighest data state threshold; and using the corrected data whilereprogramming the memory cells associated with the at least one edgeword line without erasing the memory cells associated with the at leastone edge word line.
 18. The method as set forth in claim 17, wherein thememory cells comprise a plurality of blocks, the method furtherincluding the steps of: determining whether all of the plurality ofblocks have been checked for the at least one edge word line in responseto a proactive refresh operation being triggered; ending reprogrammingthe memory cells associated with the at least one edge word line withouterasing the memory cells associated with the at least one edge word linein response to determining all of the plurality of blocks have beenchecked for the at least one edge word line; proceeding to check one ofthe plurality of blocks for the at least one edge word line in responseto determining not all of the plurality of blocks have been checked forthe at least one edge word line; determining whether each of theplurality of word lines of the one of the plurality of blocks is the atleast one edge word line and whether the memory cells connected to theat least one edge word line contain the data; returning to determiningwhether all of the plurality of blocks have been checked for the atleast one edge word line in response to determining at least one of theeach of the plurality of word lines of the one of the plurality ofblocks is not the at least one edge word line and the memory cellsconnected to the at least one edge word line does not contain the data;returning to determining whether all of the plurality of blocks havebeen checked for the at least one edge word line in response todetermining the edge higher data state quantity is not less than an edgehigher data state threshold; and returning to determining whether all ofthe plurality of blocks have been checked for the at least one edge wordline following reprogramming the memory cells associated with the atleast one edge word line without erasing the memory cells associatedwith the at least one edge word line.
 19. The method as set forth inclaim 18 further including the steps of: storing data stored informationidentifying which of the plurality of word lines are the at least oneedge word line and the plurality of other data word lines; storing edgeinformation identifying which of the memory cells connected to theplurality of word lines contain the data; and utilizing the data storedinformation and the edge information when determining whether each ofthe plurality of word lines of the one of the plurality of blocks is theat least one edge word line and whether the memory cells connected tothe at least one edge word line contain the data.
 20. The method as setforth in claim 17, wherein the plurality of data states includes a totalstate quantity of the plurality of data states.